How to convert a Map to List in Java?
What is the best way to convert a Map<key,value> to a List<value> ? Just iterate over all values and insert them in a list or am I overlooking something?
List<Value> list = new ArrayList<Value>(map.values());
假设：
Map<Key,Value> map;
The issue here is that Map has two values (a key and value), while a List only has one value (an element).
Therefore, the best that can be done is to either get a List of the keys or the values. (Unless we make a wrapper to hold on to the key/value pair).
Say we have a Map :
Map<String, String> m = new HashMap<String, String>();
m.put("Hello", "World");
m.put("Apple", "3.14");
m.put("Another", "Element");
The keys as a List can be obtained by creating a new ArrayList from a Set returned by the Map.keySet method:
List<String> list = new ArrayList<String>(m.keySet());
While the values as a List can be obtained creating a new ArrayList from a Collection returned by the Map.values method:
List<String> list = new ArrayList<String>(m.values());
The result of getting the List of keys:
Apple Another Hello
The result of getting the List of values:
3.14 Element World
使用Java 8 Streams API。
List<Value> values = map.values().stream().collect(Collectors.toList());
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